1. Field of the Invention
Both of Aspects I and II of the present invention relates to a rear-projection screen and a rear-projection display (rear-projection image display device) in which the rear-projection screen is used.
2. Related Background Art
Aspect I of the Present Invention
Needs for large screens have grown, mainly in the field of television picture tubes recently, and rear-projection displays have gained a spotlight as suitable for such a large screen. Generally, a CRT is used as an image source for the rear-projection display. Further, a type in which a spatial modulation element such as a liquid crystal element is used for advantages of lightness and compactness has been proposed and drawn attention.
First of all, the following description will depict a type in which a CRT is used as an image source. FIG. 6 is a view schematically illustrating the basic configuration of the same.
In this display, images are formed by single-color CRTs 1 (1R, 1G, and 1B) for the three main colors, respectively, and are enlarged and projected by projection lenses 2 (2R, 2G, and 2B) corresponding to the same, respectively, so as to be superimposed on a screen 3. Here, the reference codes R, G, and B correspond to red, green, and blue, respectively. As shown in the figure, light that is divergent from the center to the periphery and that partially has a sharp directivity is incident on the screen 3 disposed at the image formation plane. Besides, red, green, and blue lights incident on respective parts have angles differing from each other, respectively. The screen 3 is required to arrange such projected lights appropriately so as to allow good image recognition.
Minimum image observation is enabled by using a simple light diffusing sheet as the screen 3. Since the projected light is incident thereto divergently as described above, however, light at the peripheral part has outward directivity since the projected light is incident divergently thereon. Therefore, the brightness of the screen is remarkably uneven. For instance, the screen has an extremely low luminance at the periphery as compared with a luminance at the center when observed from the front, and has a high luminance at an end closer to the observer and a low luminance at an end farther from the observer when observed diagonally.
To avoid such unevenness, generally a Fresnel lens sheet 31 is provided on a light-projected side of a diffusing sheet. The Fresnel lens sheet 31 functions to convert the projected light divergently incident from the projection lenses 2 on the screen 3 into substantially parallel rays. By this function, green projected light is converted into parallel rays perpendicular to the screen surface, while blue and red projected lights are converted into parallel rays that are vertically parallel with each other and that have certain set angles, respectively, with respect to the normal line of the screen surface in any horizontal plane. In the case where the projected light simply is diffused in this state, the green projected light leaves the screen symmetrically with respect to the normal direction of the screen surface, while the red and blue projected lights leave the screen asymmetrically, thereby causing colors of the screen to change depending on the viewing direction. This phenomenon is called xe2x80x9ccolor shadexe2x80x9d and degrades the image quality.
To cope with this, a lenticular lens sheet 32 that has a special configuration having black stripes (BS) and pairs of lenticular lenses (this configuration is hereinafter referred to as xe2x80x9cBS Paired-Lenticular-Lens Structurexe2x80x9d) is used so as to diffuse projected light with a sharp directivity so as to make the same observable at various angles, and to suppress color shift. The function thereof is depicted with reference to FIG. 7.
FIG. 7 illustrates a cross section of the lenticular lens sheet 32 in the horizontal direction, and ray trajectories of green projected light and red projected light are indicated with a solid line (G) and a broken line (R), respectively. As shown in the figure, light-incident-side lenticular lenses 321 and light-exiting side lenticular lenses 322 that are paired are provided so that the lenses of each pair share the same optical axis. By doing so, an exiting angle of the red light that has been incident diagonally is corrected so that diffusion symmetric to the normal direction of the screen is realized, as is with the green light, whereby the color shift is suppressed. Furthermore, because light passes through limited portions of the light-exiting surface due to the light collecting function of the light-incident-side lenticular lens 321, it is possible to provide light absorbing layers 323 at light non-transmission portions of the light-exiting surface. Since the light absorbing layers are black in color and are provided in a stripe form, they are called black stripes, abbreviated as BS, and function significantly to reduce the diffusing reflection of external light incident on the screen in a bright environment, thereby improving the contrast.
It should be noted that generally the lenticular lens is formed so that its lengthwise direction is directed in the vertical direction, and the refraction by the lenticular lens affects only in the horizontal direction, and does not contribute to diffusion in the vertical direction. Therefore, light diffusing microparticles made of a material having a refractive index different from that of a base are dispersed inside the lenticular lens sheet so that light is diffused in the vertical direction. At interfaces between the base and the light diffusing microparticles, light rays are refracted depending on a refractive index difference xcex94n according to the Snell""s law, thereby being diffused isotropically. This refracting function is more intense as the difference between the refractive index of the base and that of the light diffusing microparticles is greater, which means that light is diffused more as the difference between the refractive index of the base and that of the light diffusing microparticles is greater.
Generally, a material tends to have a greater refractive index at a shorter wavelength, and this is called the wavelength dispersion of the refractive index, which is represented by an Abbe constant xcexdd. The dispersion increases and the Abbe constant xcexdd decreases as a material has a higher refractive index. The relationship between the refractive index nd of a typical material as an optical resin material and the Abbe constant xcexdd is shown in Table 1 and FIG. 10.
Thus, in order that a base and light diffusing microparticles are made of materials selected from generally-used transparent resin materials so that they have a refractive index difference xcex94n therebetween, unavoidably a high-refractive-index high-dispersion material and a low-refractive-index low-dispersion material are combined. Consequently, the refractive index difference xcex94n also is made wavelength-dependent, and hence, the refractive index difference xcex94n tends to increase as the wavelength is shorter.
In the case where the combination of the light diffusing microparticles and the base is such a combination of general materials, the refractive index difference xcex94n increases as the wavelength is shorter, thereby leading to significant diffusion. As a result, the diffusion exhibits a wavelength-dependency such that the diffusion of blue light having a shorter wavelength exceeds the diffusion of red light having a longer wavelength.
As the base material of the lenticular lens sheets, a transparent resin is used, for instance, polymethyl methacrylate (PMMA) with a refractive index of approximately 1.49, or an MS resin (copolymer of styrene and methyl methacrylate (MMA)) with a refractive index of approximately 1.52. In such a case, beads, each in a pearl form, made of an MS resin with a refractive index that is approximately 0.02 to 0.07 greater than that of the base material, are used often. The refractive index of the MS resin material used for the base material and the light diffusing microparticles can be adjusted by adjusting a mix proportion of MMA and styrene. Since the refractive index of MMA is approximately 1.49 and the refractive index of styrene is approximately 1.59, the refractive index of the MS resin can be adjusted in a range of 1.49 to 1.59. The wavelength dispersion of the MS resin increases as the refractive index nd increases (the Abbe constant xcexdd decreases as the refractive index nd increases), and this agrees with the correlation line shown in FIG. 10.
In the case where the lenticular lenses are made of materials arranged as above, the refractive index difference xcex94n between the base and the light diffusing microparticles is made wavelength-dependent for the aforementioned reasons. Therefore, the refractive index difference xcex94n increases, thereby resulting in significant diffusion, as the wavelength is shorter. Consequently, the diffusion is made wavelength-dependent, for instance, the diffusion of blue light having a short wavelength is more significant than the diffusion of red light having a long wavelength. Since light with a sharp directivity is incident on a rear-projection screen in particular, a remarkable color variation takes place in which the screen is reddish when observed from the front and becomes more bluish as the observation angle increases (as observed more diagonally). It should be noted that in the case of a rear-projection screen including lenticular lens sheets, the color variation is remarkable in the vertical direction, since the diffusion in the horizontal direction is achieved by the refracting function of the lenticular lenses.
The color variation depending on the observation angle stems from a cause different from that of the color shift due to the horizontal arrangement of the image sources of the three principal colors, and cannot be suppressed by the aforementioned BS Paired-Lenticular-Lens Structure.
Another configuration of the rear-projection screen is, as shown in FIG. 8, a configuration in which the light diffusing microparticles are not dispersed inside the lenticular lens sheet 32 but a light diffusing sheet 33 is provided on the image-observed side of the lenticular lens sheet 32. This configuration reduces optical loss that is caused by the diffusion of light inside the lenticular lens sheet 32 and the incidence of the same on the black stripes, thereby improving the efficiency and suppressing the color shift in the horizontal direction.
In this configuration also, the above-described color variation in the vertical direction due to the wavelength characteristics of the light diffusing microparticles dispersed in the light diffusing sheet 33 and the resin material used for the base tends to occur, as in the case where the light diffusing microparticles are dispersed inside the lenticular lens sheet.
Furthermore, in the type in which light from a lamp 4 is modulated by using a spatial modulation element 5 like a liquid crystal panel as an image source as schematically illustrated in FIG. 9, a single projection lens 6 is used for image projection by superimposing three principal-color images before the projection lens 6. Therefore, the aforementioned color shift correction is unnecessary. In this case, it also is proposed to use a sheet that is obtained by bonding a transparent lenticular lens sheet 34 and a light diffusing sheet 33 with each other with a transparent adhesive. The transparent lenticular lens sheet 34 has a flat light-exiting surface and is provided with black stripes (BS) on its light non-transmission portions on the light-exiting surface. In this configuration, the external light incident on the light diffusing sheet 33 is absorbed by the black stripes effectively before being diffused and reflected on its rear surface. Therefore, the contrast in a bright environment is improved.
In this configuration, the color shift in the horizontal direction does not take place, but the drawback of the color variation in the vertical direction that tends to occur when a common resin material is used still remains unsolved.
As a measure for reducing the wavelength dependency of the diffusion, a technique of combining plural kinds of light diffusing microparticles that cancel their respective wavelength dependencies of the diffusion characteristics, has been proposed; the light diffusing microparticles are, for instance, xe2x80x9clight diffusing microparticles of a higher refractive index and high dispersion than those of the base, and light diffusing microparticles of a higher refractive index and lower dispersion than those of the basexe2x80x9d (JP11(1999)-338057A). This technique allows the overall wavelength dependency of the diffusion to be suppressed, thereby realizing a configuration characterized in that the color variation depending on the observation angle is small.
The rear-projection screen sometimes is configured so that light diffusing microparticles are dispersed in a transparent base, not in order to secure an angle of visibility as described above, but in order to reduce the glaring of the screen, which is called scintillation. The scintillation is remarkable particularly in the type as shown in FIG. 9 in which the spatial modulation element 5 such as a liquid crystal panel is used. The reason for this is as follows: the projected light reaching the screen 3 has a particularly sharp directivity, because the magnification is high due to the small size of the image source as compared with the CRT projection type, and hence the projection lens 6 used therein has a great F number. In this case, the light diffusing microparticles are dispersed in the Fresnel lens sheet 31. By using this type, it is possible to reduce speckle or scintillation.
As disclosed by JP11(1999)-338057A, the use of plural kinds of light diffusing microparticles that cancel the respective dispersion wavelength-dependencies decreases the dispersion wavelength-dependency of the light diffusing sheet. In this case, however, as a material for one of the kinds of the light diffusing microparticles, a material of a higher refractive index and lower dispersion than those of the base is needed. In the case where resins are used as the base and the light diffusing microparticle material, polycarbonate or the like, apart from MMA and styrene, may be used as a transparent material applicable for an optical purpose. These resin materials, however, tend to exhibit higher dispersion as the refractive index is higher, and hence, the aforementioned combination is infeasible.
To obtain the aforementioned combination, there is no practical alternative other than the use of a transparent glass material of a higher refractive index and lower dispersion than those of a resin for forming a light diffusing microparticles of a higher refractive index and lower dispersion than those of a resin base. However, in the case where a light diffusing sheet or a rear-projection screen is produced using the light diffusing microparticles made of a glass material, damage to a cutting edge upon cutting the sheet or screen increases as compared with the case where light diffusing microparticles made of a resin material are used. Besides, there is a problem of a higher manufacturing cost as compared with the case where generally-used resin-made light diffusing microparticles are used.
In the case where light diffusing microparticles are dispersed in a Fresnel lens sheet to reduce scintillation, side effects such as the impairment of the resolving power and the decrease in the efficiency are produced. The impairment of a resolving power is caused when light diffused at one point in the Fresnel lens sheet spreads by the time it reaches the lenticular lens sheet, then again is diffused by the lenticular lens sheet. The resolving power decreases in proportion to a diffusing characteristic rendered to the Fresnel lens sheet and a distance between two diffusing elements. On the other hand, the efficiency is impaired because components lost to absorption by BS provided on the light-exiting surface of the lenticular lens sheet increase due to diffusion at the Fresnel lens sheet. The decrease in the efficiency becomes more remarkable as the diffusion at the Fresnel lens sheet becomes more significant.
Aspect II of the Present Invention
Needs for large screens have grown mainly in the field of television picture tubes recently, and rear-projection displays have gained a spotlight as suitable for such a large screen. Generally, a CRT is used as an image source for the rear-projection display, but a device making use of light modulation by a liquid crystal panel or the like has been developed and is expected to realize further lightness and compactness. A basic configuration of the same is shown schematically in FIG. 16.
Light emitted from a lamp 4 is subjected to spatial modulation by the liquid crystal panel 5 so that an image is formed, and the image is enlarged and projected by a projection lens 6. It should be noted that an actual device generally is provided with three liquid crystal panels to obtain color display, and in this case, the device has a complex structure including a color separation optical system for separating the light from the lamp 4 into red, green and blue components, a color synthesizing optical system for synthesizing lights that has passed through the three liquid crystal panels, and the like. However, these are omitted herein.
Furthermore, examples of similar types making use of spatial modulation include a type utilizing a reflective liquid crystal element as a modulating element, and a type utilizing a multiplicity of micromirrors whose angles are variable (micromirror device).
Light that is divergent from the center to the periphery and that partially has a sharp directivity is incident on the rear-projection screen 3 disposed at the image formation plane. The degree of the directivity is represented by a projection directivity angle xcex8, which is expressed as:
xcex8=tanxe2x88x921[1/{2xc3x97Fxc3x97(M+1)}]≈1/{2xc3x97Fxc3x97(M+1)}
where M represents a projection magnifying power M and F represents an F number of the projection lens.
It should be acknowledged that in a device utilizing a CRT as an image source, the projection magnifying power M for a display with a diagonal of the 50-inch order is approximately 10 since a CRT with an about 5-inch diagonal is used, and the F number is set as small as approximately 1 so that diffused light from a fluorescent body is captured. Consequently, a projection directivity angle xcex8 of approximately 0.05 (about 3xc2x0) is obtained.
On the other hand, in a type utilizing an image modulating element such as a liquid crystal panel, the F number of the projection lens is as great as 3 since an element with a diagonal of approximately 1 inch is used and illuminating light with a relatively high directivity needs to be used in view of the characteristics of the element. Therefore, the projection directivity angle xcex8 is as small as approximately 0.003 (about 0.2xc2x0), and projected light incident on the screen has an extremely strong directivity.
The screen 3 functions to arrange such projected light appropriately so as to enable good image recognition.
Even in the case where a simple diffusing means (diffusing plate) is used as the screen 3, the minimum image observation is enabled. However, since the projected light is incident divergently as described above, the light has an outward directivity at the peripheral part, thereby causing remarkable unevenness in the brightness of the screen. For instance, the screen 3 has an extremely low luminance at the periphery as compared with a luminance at the center when observed from the front, and it has a high luminance at an end closer to the observer and a low luminance at an end farther from the observer when observed diagonally.
To avoid such unevenness, generally a Fresnel lens sheet 35 is provided on a light-projected side of a diffusing means.
The Fresnel lens sheet 35 functions to convert the projected light divergently incident from the projection lens 6 on the screen 3 into parallel rays with a principal directivity that is substantially perpendicular to the screen surface.
Thus, if the light is diffused after having been converted into light with a principal directivity perpendicular to the screen surface at any part of the screen, it is possible to obtain substantially uniform brightness throughout the whole screen, irrespective of the direction in which the screen is viewed.
Furthermore, generally a laminated lenticular lens sheet 36 is used as the diffusing means, instead of a simple isotropic diffusing plate.
Considering the observation range, the image recognition at various angles need to be achieved as to the observation range in the horizontal direction, whereas the image recognition only in the standing state and in the sitting state suffices as to the observation range in the vertical direction. Therefore, it is possible to provide an evenly bright image by effectively allocating light to necessary regions by anisotropic diffusion. The laminated lenticular lens sheet 36 provides the anisotropic diffusion.
The laminated lenticular lens sheet 36 is composed of a BS (black stripe)xe2x80x94provided lenticular lens film 362, and a diffusing sheet 361 obtained by integrally providing a light diffusing layer 3612 and a transparent layer 3611. As shown in FIG. 17, the lenticular lens film 362 has lenticular lenses 3621 provided on a light-incident-side surface thereof whose lengthwise direction is directed in the vertical direction. The lenticular lens film 362 has a thickness set so that the focus position of each lenticular lens 3621 substantially coincides with the light-exiting surface of the film. Therefore, the projected light incident on the lenticular lens film 362 is converged in the vicinity of the light-exiting surface, and then, exits therefrom. On the light-exiting surface of the lenticular lens film 362, light non-transmission regions that the projected light does not pass through and whose lengthwise direction is directed in the vertical direction are provided in a stripe form. On the light non-transmission regions, light absorbing layers (black stripes: BS) 3622 are provided in a stripe form. The light-exiting surface of the BS-provided lenticular lens film 362 and the diffusing-layer-3612-side surface of the diffusing sheet 361 are made to adhere to each other with a transparent adhesive or a transparent bonding material 363.
As shown in FIG. 17, an array pitch P1 of the lenticular lenses 3621 on the lenticular lens film 362 preferably is as small as possible so that the moirxc3xa9 effect caused by the lenses and the pixels is suppressed and that a high resolving power is obtained. In order to decrease the pitch P1, it is necessary to decrease the pitch at which the black stripes 3622 are provided on the light non-transmission regions on the light-exiting surface of the lenticular lens film. Conventionally it has been difficult to provide the black stripes precisely at a fine pitch on the light non-transmission regions. Now, however, a technique of selective exposure by making use of the light collecting function of the lenticular lenses has been developed, so that a fine pitch at a level of not more than 0.2 mm is obtained. In this case, the lenticular lens film 362 has a thickness t1 of not more than 0.3 mm so as to obtain a diffusion angle required of the lenticular lens film 362 and to collect light onto the light-exiting surface.
The diffusing sheet 361 is made of, as a base, a transparent material such as polymethyl methacrylate (PMMA), or an MS resin (copolymer of styrene (refractive index: 1.59) and methyl methacrylate (MMA, refractive index: 1.49)), and only in the diffusing layer 3612 part in the diffusing sheet 361, the light diffusing microparticles having a refractive index slightly greater than the refractive index of the transparent material forming the foregoing base are dispersed. The thickness of the diffusing sheet 361 generally is about 2 mm so as to obtain a mechanical strength that allows the whole laminated lenticular lens sheet 36 to be maintained stably, while the thickness of the diffusing layer 3612 and the thickness of the transparent layer 3611 are set to about 0.1 mm to 0.2 mm, and about 1.0 mm to 1.8 mm, respectively.
It should be noted that it is possible to obtain an identical diffusing function by not making the diffusing sheet in a two-layer structure, but dispersing the diffusing material throughout the thickness thereof of approximately 2 mm. This, however, is inferior to the above-described two-layer structure with respect to the resolving power, and particularly in the case where a great diffusion characteristic is imparted so that the angle of visibility is increased, significant deterioration of the resolving power tends to occur.
With the configuration as above, the projected light that has been converted by the Fresnel lens sheet 35 into substantially parallel light is diffused to a relatively wide range in the horizontal direction by the synergism of the refractive effect of the lenticular lenses 3621 and the light diffusing microparticles in the diffusing layer 3612, while it is diffused in a relatively narrow range in the vertical direction only by the effect of the light diffusing microparticles in the diffusing layer 3612. Thus, the aforementioned anisotropic diffusion is realized.
As to the rear-projection display in which a light modulation element as described above is used, a phenomenon called scintillation has emerged, which was not apparent in a device utilizing a CRT as an image source. The scintillation is a phenomenon in which glaring occurs on a screen due to minute light and dark patterns, and it also is called speckle.
The reason why scintillation particularly becomes apparent in the rear-projection display utilizing a light modulation element is that the directivity of the projected light incident on the screen is significantly more intense as compared with that of a display utilizing a CRT as described above, thereby producing high spatial coherence that leads to mutual interference of light diffused by the light diffusing microparticles.
JP8(1996)-313865A proposes, as a technique for suppressing scintillation, to provide two layers of diffusing elements with a certain set distance therebetween. In this case, generally, the laminated lenticular lens sheet in which generally the light diffusing microparticles are dispersed is utilized as the diffusing element, and in addition to that, the Fresnel lens sheet 35, which is a basic element of the screen like the laminated lenticular lens sheet, is utilized also as the diffusing element.
In JP10(1998)-293361A and JP10(1998)-293362A, an appropriate diffusion characteristic to be imparted to the Fresnel lens sheet is defined with a haze value.
Thus, the dispersion of the light diffusing microparticles not only in the laminated lenticular lens sheet 36 but also in the Fresnel lens sheet 35 makes it possible to suppress scintillation. At the same time, however, it produces unfavorable side effects as a rear-projection display.
One of the side effects is as follows: among the light diffused by the Fresnel lens sheet 35, components incident on the laminated lenticular lens sheet 36 at relatively great angles are absorbed by the black stripes 3622 provided on the lenticular lens film 362, thereby being lost.
Scintillation is suppressed more effectively as the diffusion characteristic imparted to the Fresnel lens sheet 35 increases, but the aforementioned absorption loss increases as the diffusion characteristic increases.
Another side effect is a drawback in that the resolving power significantly deteriorates when a gap is produced between the Fresnel lens sheet 35 and the laminated lenticular lens sheet 36.
The Fresnel lens sheet 35 and the laminated lenticular lens sheet 36 tend to warp in response to changes in the ambient temperature and moisture, since they usually are made of a resin. A technique of previously making the both warped so as to cause the same to adhere closely and fixing the peripheral part of the same is available to prevent a gap from being produced between the Fresnel lens sheet 35 and the laminated lenticular lens sheet 36 due to such environmental changes. With the use of such a technique, however, it still is difficult to completely prevent such a gap from being produced under readily conceivable environmental changes.
Furthermore, in the case where the laminated lenticular lens sheet 36 and the Fresnel lens sheet 35 are thus warped previously, the screen surface is warped in a state of being mounted on the device. In such a state, the projection magnifying power varies depending on a position, and such a projection magnifying power distribution causes a projected image to be deformed. Besides, the reflection image of external light also is caused to have deformation, which makes an undesirable appearance, particularly when the device is turned off.
Aspect I of the Present Invention
Therefore, with the foregoing in mind, it is a first object of the aspect I of the present invention to provide a rear-projection screen with small wavelength dependency of diffusion characteristics, which can utilize resin materials with general properties, with the aforementioned problems being solved.
It is a second object of the aspect I of the present invention to provide a rear-projection screen in which scintillation is suppressed while the side effects caused by the diffusion by the Fresnel lens sheet are suppressed.
It also is a still another object of the aspect I of the present invention to provide a rear-projection display in which the foregoing rear-projection screen is used.
To achieve the foregoing first object, in a rear-projection screen according to the aspect I of the present invention, light diffusing microparticles dispersed inside as a diffusing element are arranged so that the product of a refractive index difference xcex94n from the base material and an average particle diameter d, that is, xcex94nxc3x97d, is in a range of 0.5 to 0.9. This makes it unnecessary to use light diffusing microparticles made of a material with specific characteristics, for instance, a higher refractive index and high dispersion than those of the base material, or a higher refractive index and lower dispersion than those of the base material. This allows light diffusing microparticles made of a general resin material to be used for achieving diffusion characteristics with small wavelength dependency.
Furthermore, to achieve the foregoing second object, in a rear-projection screen according to the aspect I of the present invention, light diffusion by light diffusing microparticles dispersed in a Fresnel lens sheet is made smaller than light diffusion by light diffusing microparticles dispersed in a light diffusing sheet or a lenticular lens sheet, and the light diffusing microparticles dispersed in the Fresnel lens sheet are arranged so that the aforementioned xcex94nxc3x97d is in a range of 0.1 to 0.3. This allows scintillation to be suppressed effectively, while reducing side effects such as a decrease in the resolving power, optical loss, etc.
Furthermore, since a rear-projection display according to the aspect I of the present invention is provided with the rear-projection screen according to the aspect I of the present invention, an image display that undergoes a minimum of color tone variation depending on an observation direction, exhibits a minimum of scintillation and excels in resolution can be achieved.
Aspect II of the Present Invention
It is an object of the aspect II of the present invention to provide a rear-projection screen in which the aforementioned problems are solved, scintillation is minimized, loss due to absorption by black stripes is reduced, and a resolving power is not significantly impaired in response to ambient changes, and also to provide a rear-projection display in which the foregoing rear-projection screen is used.
To achieve the foregoing object, a rear-projection display and a rear-projection screen according to the aspect II of the present invention are configured so that a diffusing layer provided in a laminated lenticular lens sheet is positioned apart from a focal plane of a lenticular lens sheet and in a predetermined range that is effective for suppressing scintillation and reducing a decrease in the resolving power. Furthermore, preferably a transparent Fresnel lens sheet containing substantially no diffusing material is used.
More specifically, a first rear-projection display according to the aspect II of the present invention includes a spatial modulation element, and a rear-projection screen on whose surface on a light-projected side an image formed by the spatial modulation element is projected so that the image is observed from an image-observed side opposite to the light-projected side. In the rear-projection display, the rear-projection screen includes a first screen element for converting projected light from the spatial modulation element into substantially parallel light, and a second screen element for diffusing the substantially parallel light. The second screen element includes a lenticular lens array that is provided on the surface on the light-projected side and whose lengthwise direction is directed in a vertical direction, a diffusing layer provided on the image-observed side to the lenticular lens array, and a transparent layer provided between the lenticular lens array and the diffusing layer. In this, a distance t1 between a light-projected-side surface of the diffusing layer and a focal plane of the lenticular lens array satisfies Formula II-1 below, and a distance t2 between an image-observed-side surface of the diffusing layer and the focal plane of the lenticular lens array satisfies Formula II-2 below:
t1xe2x89xa7f1xe2x80x83xe2x80x83Formula II-1 
t2xe2x89xa6f1xc3x97Pg/P1xe2x80x83xe2x80x83Formula II-2 
where f1 represents a distance between a valley of the lenticular lens array and the focal plane, Pg represents a pixel pitch on the screen, and P1 represents an array pitch of the lenticular lens array.
With the foregoing first rear-projection display, scintillation can be reduced by satisfying Formula II-1, and a high resolving power can be obtained by satisfying Formula II-2.
Furthermore, a second rear-projection display according to the aspect II of the present invention may be configured so that the distance t2 between an image-observed-side surface of the diffusing layer and the focal plane of the lenticular lens array satisfies Formula II-3 below, in place of Formula II-2 for the first rear-projection display:
t2xe2x89xa6Pg/2/tan(xcex3i)xe2x80x83xe2x80x83Formula II-3 
where xcex3i represents an in-layer equivalent angle in the transparent layer that is obtained by converting an observation angle xcex3 at which a luminance of {fraction (1/10)} of that in a normal direction is obtained due to diffusion caused by the diffusing layer, and is expressed as Formula II-4 below:
xcex3i=a sin(sin(xcex3)/n)xe2x80x83xe2x80x83Formula II-4 
where n represents a refractive index of the transparent layer.
With the foregoing second rear-projection display, scintillation can be reduced by satisfying Formula II-1, and a high resolving power can be obtained by satisfying Formula II-3.
Next, a first rear-projection screen according to the aspect II of the present invention is a rear-projection screen on whose surface on a light-projected side an image formed by a spatial modulation element is projected so that the image is observed from an image-observed side opposite to the light-projected side. The rear-projection screen includes a first screen element for converting projected light from the spatial modulation element into substantially parallel light, and a second screen element for diffusing the substantially parallel light. The second screen element includes a lenticular lens array that is provided on the surface on the light-projected side and whose length-wise direction is directed in a vertical direction, a diffusing layer provided at the image-observed side of the lenticular lens array, and a transparent layer provided between the lenticular lens array and the diffusing layer. In this, a distance t1 between a light-projected-side surface of the diffusing layer and a focal plane of the lenticular lens array satisfies Formula II-1 below, and a distance t2 between an image-observed-side surface of the diffusing layer and the focal plane of the lenticular lens array satisfies Formula II-5 below:
t1xe2x89xa7f1xe2x80x83xe2x80x83Formula II-1 
t2xe2x89xa6f1xc3x97P1xc3x970.7xe2x80x83xe2x80x83Formula II-5 
where f1 represents a distance between a valley of the lenticular lens array and the focal plane, and P1 represents an array pitch of the lenticular lens array, the unit of t1 is according to that of f1, and the unit of t2 is millimeters.
With the foregoing first rear-projection screen, scintillation can be reduced by satisfying Formula II-1, and a high resolving power can be obtained by satisfying Formula II-5.
Furthermore, a second rear-projection screen according to the aspect II of the present invention may be configured so that the distance t2 between an image-observed-side surface of the diffusing layer and the focal plane of the lenticular lens array satisfies Formula II-6 below, in place of Formula II-5 for the first rear-projection screen:
xe2x80x83t2xe2x89xa60.35/tan(xcex3i)xe2x80x83xe2x80x83Formula II-6
where f1 represents a distance between a valley of the lenticular lens array and the focal plane, and xcex3i represents an in-layer equivalent angle in the transparent layer that is obtained by converting an observation angle xcex3 at which a luminance of {fraction (1/10)} of that in a normal direction is obtained due to diffusion caused by the diffusing layer, and is expressed as Formula II-7 below:
xcex3i=a sin(sin(xcex3)/n)xe2x80x83xe2x80x83Formula II-7 
where n represents a refractive index n of the transparent layer, and the unit of t1 is according to that of f1, and the unit of t2 is millimeters.
With the foregoing second rear-projection screen, scintillation can be reduced by satisfying Formula II-1, and a high resolving power can be obtained by satisfying Formula II-6.